Ion diffusion in a velocity space induced by Alfven ion cyclotron mode observed in a mirror plasma

Ion distributions in a loss cone are measured in the GAMMA 10 tandem mirror [Phys. Rev. Lett. 55, 939 (1985)]. When Alfven ion cyclotron (AIC) modes a re excited in the central cell, enhanced end-loss of ions is observed for a characteristic energy region which agrees well with the resonant ion cyclo tron condition with the AIC wave. From measurements of pitch angle distribu tions of end-loss ions, it is found that the loss cone is filled for this c haracteristic energy region, indicating an ion diffusion in a velocity spac e induced by the AIC wave. Magnitude of the observed additional end-loss in creases with increase in the amplitude of the AIC modes. In the present exp erimental parameters in GAMMA 10, the AIC wave effect on the axial ion conf inement is not serious. (C) 2000 American Institute of Physics. [S1070-664X (00)02706-3].